docs: def _compute_logarithmic_distance_term(self, C, mag, dists):
          """
          Compute and return fourth term in equations (2a)
          and (2b), page 20.
          """
          return (
              (C['a4'] + C['a5'] * (mag - self.c1)) *
              np.log(np.sqrt(dists.rhypo ** 2 + C['a6'] ** 2))
          )